It has been well known that it is desirable to make pressure measurements in vessels and particularly in coronary arteries with the advent of angioplasty. Typically in the past, such pressure measurements have been made by measuring the pressure at a proximal extremity of a lumen provided in a catheter advanced into the coronary artery of interest. Such an approach has, however, been less efficacious as the diameters of the catheters became smaller with the need to advance the catheter into smaller vessels and to the distal side of atherosclerotic lesions. This made necessary the use of smaller lumens that gave less accurate pressure measurements and in the smallest catheters necessitated the elimination of such a pressure lumen entirely. Furthermore, the catheter is large enough to significantly interfere with the blood flow and damp the pressure resulting in an inaccurate pressure measurement. In an attempt to overcome these difficulties, ultra miniature pressure sensors have been proposed for use on the distal extremities of a guidewire. Using a guidewire with a smaller diameter is less disruptive to the blood flow and thus provides an accurate pressure reading. Currently, the use of two sensors on the distal region of a guide wire has been proposed, such as, e.g., the use of flow sensor, for example, an ultrasound transducer or Doppler flow sensor, disposed near the distal tip of the guide wire in conjunction with a pressure sensor located proximally from the ultrasound transducer.
The current designs require a separation between the ultrasound transducer and the pressure sensor, which for some designs may be approximately 3 cm. As a result, the current designs do not allow a user to take both Doppler flow measurements using the ultrasound transducer and pressure measurements using the pressure sensor at substantially the same time at the same location, or to take both measurements near the distal tip of the guide wire. For example, because the pressure sensor is located proximal from the ultrasound transducer, the currently proposed designs require a user to advance the guide wire to a desired location, obtain a Doppler flow measurement with the ultrasound transducer, and then advance the guide wire further distally in order to obtain a pressure measurement using the pressure sensor at the same location. The additional distal movement of the guide wire using the current designs is undesirable as such movement may inflict trauma (or further trauma) to the body, such as, e.g., to the arterial walls. Another disadvantage of the separated placement of the ultrasound transducer and the pressure sensor on currently proposed designs is that there may be a limit as to how far distally a measurement may be taken with the guide wire. For example, the currently proposed designs are not able to take a measurement at the extreme distal end of a cavity or body lumen because there is no room to maneuver the pressure sensor distally to the desired location once the distal end of the guide wire is in physical contact with the distal end of the body lumen. Also, when attempting to advance one sensor to the location at which a measurement was already taken with the other sensor, it is difficult to know the exact location to stop the advancement. It has not, however, been feasible prior to the present invention to provide for two different sensors, such as, e.g., both an ultrasound transducer and a pressure sensor, in close proximity to each other near the distal tip of a guide wire. There is therefore a need for a new and improved ultra miniature pressure and flow sensor, as well as a guide wire and apparatus for utilizing the same.
In order to provide measurement data to a user, the guide wire must be coupled to a physiology monitor located at the user's end. Unfortunately, the current methods for coupling and decoupling the guide wire directly to the physiology monitor or to a cable leading to the physiology monitor are deficient in certain respects.
For example, the guide wire comprises basically a core wire and a plurality of electrical conductors disposed within an elongate tubular member for transferring electrical signals from the sensors located at the distal end of the guide wire. Usually three electrical conductors are necessary for a stand alone pressure measurement guidewire and two electrical conductors are necessary for a stand alone flow sensor guidewire, thus in a combination guide pressure and flow measurement guidewire, five electrical conductors are required. These electrical conductors extend through the lumen from the pressure and flow sensors at the distal end of the tubular member to a male connector located at the proximal end of the guidewire for electrically and mechanically connecting to a female connector, for example on a physiology monitor or a cable. During connection, there is a substantial risk that the proximal end of the guidewire and/or male connector may be bent and the electrical connections may be damaged. Thus it is desired that the proximal portion of the guidewire is as stiff as possible for pushability, handling, kink resistance and catheter support. It is also desirable that the male connector portion is as stiff as possible to aid in the attachment and detachment of the male connector to the female connector/cable. In traditional guide wires, the electrical conductors extend in the space between a stainless steel core wire and the outer elongate tubular member, usually stainless steel. The stiffness of the guidewire is due for the most part to the dimensional and material properties of the core wire and the tubular member, specifically diameter and thickness of the core wire and tubular walls. However, these properties are limited by the need to electrically insulate the electrical conductors and to ensure that the electrical conductors have enough space to freely extend without damage. The use of five electrical conductors in a combination pressure and flow sensor guidewire, instead of the traditional two or three conductors for stand alone flow or pressure sensor guidewires, further complicates the solution.
Additionally, the use of traditional rotary connectors to connect the guidewire to the physiology monitor may render the guide wire awkward to manipulate and often require high insertion forces to place the guide wire in the connector. These traditional connectors also exhibit a high degree of torsional resistance, which also increases the difficulty of manipulating the guide wire within the body.
In general it is an object of the present invention to provide an ultra miniature pressure sensor, ultrasound transducer and guide wire and apparatus utilizing the same, making possible pressure and velocity measurements using a pressure sensor and an ultrasound transducer located in close proximity to each other on or near the distal end of the guide wire.
Another object of the present invention is to provide for increased stiffness in the proximal end of the guidewire to increase the catheter support, handling, kink resistance and pushability of the guidewire and decrease the risk of bending the proximal end of the guidewire or damaging the electrical connectors inside of the guidewire.
Another object of the present invention is to provide for improved methods for coupling a guide wire to a physiology monitor or cable that increase the ease of connecting the guide wire to the monitor as well as increase the ease of manipulating the guide wire within the body.
Additional features and objects of the invention will appear from the following description in which the preferred embodiments are set forth in detail in conjunction with the accompanying drawings.